1. Field of the Invention
The present invention relates to an ink for ink jet recording which can produce high-quality printed images on various recording media, and an ink jet recording method using the same.
2. Background Art
Ink jet recording is a method wherein an ink is ejected as droplets through fine nozzles to record letters or figures onto the surface of recording media. Ink jet recording systems which have been developed and put to practical use include: a method wherein an electric signal is converted to a mechanical signal using an electrostrictive element to intermittently eject an ink reservoired in a nozzle head section, thereby recording letters or symbols on the surface of a recording medium and a method wherein an ink, reservoired in a nozzle head section, in its portion very close to the ejection portion is rapidly heated to create a bubble and the ink is intermittently ejected by volume expansion created by the bubble to record letters or symbols on the surface of a recording medium.
Properties required of inks used in the above ink jet recording are such that the drying property of the print is good, no feathering is created in prints, good printing can be performed on various recording media, and, in the case of multi-color printing, color-to-color intermixing does not occur.
In particular, prevention of feathering is important for realizing high-quality images. Paper is likely to create feathering because it comprises fibers that are different from one another in ink penetration. In particular, this tendency is significant for recycled paper because it comprises various fibers having different ink penetration. For this reason, in order to prevent the feathering, various proposals have been made on a reduction in penetration of the ink into recording media or an improvement in drying speed of the printed ink image.
For example, Japanese Patent Publication 2907/1990 proposes utilization of glycol ether as a wetting agent, Japanese Patent Publication 15542/1989 proposes utilization of a water-soluble organic solvent, and Japanese Patent Publication 3837/1990 proposes utilization of a glycol ether as a dye solubilizer.
Further, in order to improve the penetrability of an ink for ink jet recording, U.S. Pat. No. 5,156,675 proposes addition of diethylene glycol monobutyl ether, U.S. Pat. No. 5,183,502 proposes addition of surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd.) as an acetylene glycol surfactant, and U.S. Pat. No. 5,196,056 discloses addition of both diethylene glycol mono-n-butyl ether and Surfynol 465. Furthermore, U.S. Pat. No. 2,083,372 studies and teaches utilization of an ether of diethylene glycol in an ink. In this connection, diethylene glycol mono-n-butyl ether is known as butylcarbitol to those skilled in the art, and detailed description thereon is given, for example, in U.S. Pat. No. 3,291,580.
Regarding means for regulating the penetrability of the ink using a pigment, for example, Japanese Patent Laid-Open No. 147861/1981 discloses utilization of a pigment and triethylene glycol monomethyl ether in combination. Japanese Patent Laid-Open No. 111165/1997 discloses utilization of a pigment and an ether of ethylene glycol, diethylene glycol, or triethylene glycol in combination.
On the other hand, a method has been proposed wherein an ink is printed on a heated recording medium to rapidly evaporate the solvent component, thereby permitting the ink to be rapidly fixed onto the recording medium. Heating, however, is likely to have an adverse effect on recording media, particularly paper. Further, this method involves an additional disadvantage of increased power consumption by heating.
The present inventors have now found that an ink comprising a compound having a specific structure, when used in ink jet recording, can realize good images having good drying speed and no significant feathering on various recording media, especially recycled papers.
Accordingly, it is an object of the present invention to provide an ink that can realize good images on various recording media, especially plain papers.
Thus, according to one aspect of the present invention, there is provided an ink for ink jet recording, comprising at least a water-soluble colorant, a water-soluble organic solvent, water, and a mixture of two or more compounds represented by formula (I):
Rxe2x80x94([(EO)n-(PO)m]-T)kxe2x80x83xe2x80x83(I) 
wherein
EO represents an ethyleneoxy group;
PO represents a propyleneoxy group;
T represents an OH group or SO3M wherein M represents a hydrogen atom, an alkali metal, an inorganic base, or an organic amine;
m and n are each an integer;
k is a natural number of not less than 1;
R represents
a CaH2a+2xe2x88x92k group where a represents natural number of 4 to 10,
an Raxe2x80x94CaH2a+1xe2x88x92k group where a represents natural number of 4 to 10 and Ra represents a group represented by formula
(Txe2x80x94[(PO)mxe2x80x2-(EO)nxe2x80x2])k- 
wherein
EO, PO, T and k each are as defined above; and nxe2x80x2 and mxe2x80x2 are respectively n and m,
EO and PO being arranged, regardless of order in the parentheses, randomly or as blocks joined together,
n or n+nxe2x80x2 being 1 to 10 with m or m+mxe2x80x2 being 0 to 5 when n and m and nxe2x80x2 and mxe2x80x2 are expressed in terms of the average value for the mixture of compounds represented by formula (I) contained in the ink, or
a group represented by the following formula;
Kxe2x80x94Mxe2x80x94Oxe2x80x94
wherein K represents a saturated or unsaturated aromatic ring having 4 to 15 carbon atoms or a saturated or unsaturated aliphatic ring having 4 to 15 carbon atoms, M represents a bond or an alkylene group having 1 to 12 carbon atoms, and O represents an oxygen atom.